Most of the industrial wastewaters comprise toxic, biologically non-biodegradable, and heavy metals which tend to accumulate in the biological organisms causing different diseases. There are some novel technologies and strategies to remove these pollutants. Using the magnetic nanoparticles which are cheap, recyclable, and reusable can be considered as an effective method for removing the pollutants as they do not require conservation or complicated equipments. Using this method, dangerous and rare heavy metals can be restored to the industry. In this study, magnetic nanoparticles with the size of 30 nm were prepared and used for the removal of chromium from synthetic wastewater polluted by chromium sulfate. For this purpose, removal of various concentrations of chromium(III) from wastewater was investigated. The best concentration was achieved in the removal efficiency of 99.1 %. The optimal values of pH, rotation speed of magnetic stirrer, time, temperature, and the amount of nanoparticles were determined according to the primary concentration (500 mg/L). The mechanism of chromium adsorption onto iron oxide (Fe 3 O 4 ) magnetic nanoadsorbent was also investigated. The results showed both Freundlich and Longmuir isotherms to be the best fit for the chromium adsorption, with Freundlich isotherm being more suitable.

In the present study, electrocoagulation-flocculation method was used to treat the wastewater from Shazand Oil Refinery in Arak, Iran. The wastewater contained 170,000 mg/L COD and 5.3 mg/L lead (Pb). In each step of the experiment, 2 L of the refinery wastewater was poured into a pilot made up of Plexiglas, and bipolar electrode arrangement was used. Optimum values of time, pH, and voltage parameters were determined for the aluminum electrodes. Results showed that time duration of 90 m, pH of 6, and voltage of 30 V was suitable for the removal of lead and COD. It should be noted that 48% of COD was removed and lead concentration decreased from 5.3 mg/L to lower than 0.05 mg/L. In addition, the COD removal efficiencies were 56 and 64% for eight and ten aluminum electrodes, respectively. The effect of iron electrodes on the removal of COD and lead was investigated under the same optimum conditions. Comparison between iron and aluminum electrodes indicated that iron electrodes demonstrate a better efficiency by removing 66.94% of COD from wastewater. It was also found that pH played a significant role in pollutants removal due to the formation of aluminum hydroxide gelatinous polymer.

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